We
present a new technique of injecting clocks optically onto CMOS chips
without the use of a receiver amplifier. We discuss the benefits of
such a direct approach and present proof-of-principle experiments of
the technique. We analytically compare a receiver-less optical clock
distribution and an electrical clock distribution in a fan-out-of-four
clock tree to evaluate the timing and power benefits of the optical
approach for present microprocessors. We also compare receiver-less
direct injection of optical clocks to trans-impedance receiver based
injection within the same distribution framework.